Vacuum tube



w. L. KRAHL VACUUM TUBE Filed June 6. 1928 INVENTOR 01/75 KRIH/L Mun-R A ATTORNEY Patented Apr. 28, 1931 UNITED STATES PATENT ()FFICE WALTER LOUIS KRAHL, OF MON TCLAIR, NEW JERSEY, ASSIGNOR TO ARGT'URUS RADIO TUBE COMPANY, OF NEWARK, NEW JERSEY, A CORPORATION OF DELAWARE VACUUM TUBE Application filed June 6, 1928.

This invention relates to vacuum tubes and particularly to vacuum tubes of the heater type.

In the manufacture of radio tubes there are two types which may be used in connection with alternating current, one being the heater type tube which has an independent cathode heated by a filament energized by alternating current, and the other is a tube in which the cathode is heated by current flowing through the cathode itself. In this latter type of tube, in order to eliminate the hum due to the difi'erence in potential between the ends of the filament it has been found desirable to make the grid return connection to the midpoint of the filament. If the grid return is made directly to the filament, this necessitates a fifth terminal on the base of the tube, and therefore, a special socket must'be provided for this type of tube. In order to eliminate the use of a fifth terminal it has been found advantageous to connect a potentiometer.

across the filament leads of the tube and to connect the grid return circuit to the midpoint of the potentiometer, which accomplishes the same result as though the grid return circuit were connected to the center point of the filament. In some circuits designed for the use of these tubes there is provided a potentiometer across the filament leads with the grid return circuit connected to the center point thereof, and hence it is impossible to use any other type of tube in the circuit except that employing three elements as described above.

It is one of the objects of the present invention, therefore, to provide a heater type tube for alternating current which may be used to replace the three element alternating current tube referred to above.

Another object of the invention is to provide a heater type tube having the cathode connected within the tube to a point on the heater circuit corresponding in effect to the mid-point of the heater.

Another object of the invention is to provide a heater type tube in which a potentiometer is connected across the filament leads inside of the base of the tube and the cathode Serial No. 283,441.

connected to the center point of this potentiometer.

Other objects of the invention will be apparent as the description thereof proceeds.

One embodiment of the invention has been illustrated in the accompanying drawings; in which The figure shows a perspective View of a tube embodying the invention with a portion of the tube broken away for clearness and indicating the adaptation of the invention to the circuit.

The invention is'shown in connection with an envelope 10 having the usual base 11 upon which the terminals 12 for making the necessary connections are mounted. The elements of the tube are mounted upon the stem 13 and comprise a plate 14, a grid, 15, a cathode l6, and a heater 17 which is supported adjacent the cathode and has independent connections comprising the support 18 and the conductor 19 which pass through the press 13 and are connected by means of wires 20 and 21 respectively to the heater terminals 22 and 23.

Inside of the base 11 of the tube I have provided a potentiometer 24, which preferably comprises a coil 25 of resistance wire wound upon a fiat strip 26 of insulation material which is bent, after winding, to fit the inner surface of the base of the tube. The ends 27 and 28 of the coil 25 are connected respectively to the filament terminals 22 and 23 while a center tap 29 connected to the midpoint thereof is connected by means of a wire 30 passing through the press to the conductor 31 supporting the lower end of the cathode 16.

It will be evident from this description that the potentiometer 2% is connected across the heater leads 20 and 21 within the base of the tube and the cathode 16 is separately con nected to the mid-point 29 of the potentiometer.

This tube is adapted to be inserted in a circuit in which a potentiometer 32 is connected between the two filament leads 33 and 3-5: which lead to the secondary 35 of a transformer 36, the primary 37 of which is adapted to be connected across the alternating current power source 38, and the grid return circuit comprising a common lead 39 is connected to the mid-point of the potentiometer 32. When the tube comprising the invention is used with this circuit it will be evident that the voltage drop in the potentiometer 32 from the center to either end thereof will be balanced by the voltage drop in the potentiometer 24 so that the cathode will be maintained at a potential corresponding to the average potential of the filament or a potential which is substantially the same as that at the mid-point of the filament.

The invention permits, therefore, the manufacture of a heater type tube which has certain advantages over the three element tube to replace a three element alternating current tube in a circuit designed especially for the latter.

lVhile I have shown and describedone embodiment of the invention, it is evident that certain changes may be made, especially in the construction of the potentiometer, and I do not, therefore, desire to limit myself to the specific construction shown but to interpret the invention broadly within the scope of the appended claims.

What I claim is:

1. In a vacuum tube of the heater type, a tubular cathode, .a single straight heater for said cathode, and meanscontained Within the base of the tubeto connect said cathode to a point electrically connected to the heater circuit vbut spaced from the heater itself and having a potential equal to the average a1- ternating-potential of the heater.

2. In a vacuum tube of the heater type, a cathode, a heater adjacent said cathode and independent thereof, a connection from the upper end of said heater, a connection from the lower end of said heater, a high resistance connected between said heater connections, and a connection from the mid-point of said high resistance to said cathode, said high resistance and connections being contained within the base of said tube.

3. In a vacuum tube of the heater type, a cathode, a heater for said cathode, a connection for the lower end of said heater, a connection for the upper end of said heater, a potentiometer within the base of said tube comprising a strip of insulating material and a coil of high resistance wire wound upon said strip, connections between the ends of said potentiometer coil and said heater connections, and a connection from the mid-point of said potentiometer coil to said cathode.

4. In a vacuum tube of the heater type, an envelope, a base on said envelope, filament terminals mounted upon said base, a cathode Within said envelope, a heater adjacent said cathode,a connection from one end of said heater extending down into said base and connected to oneof said terminals, aconnection from the other end of said heater extending down into said base and connected to the other of said terminals, a potentiometer, means to connect said potentiometer between said terminals, and means to connect said cathode to the mid-point of said potentiometer, said potentiometer being enclosed within said base.

5. In a vacuum tube of the heater type, an

envelope, a base mounted upon said envelope,

heater terminals mounted on said base, a cathode within said envelope, a. heater adjacent said cathode, a connection from one end of said heater to one of said heater terminals .on said base, a connection between the other end of said heater and the other of said heater terminals, a strip of insulating material within said base curved to substantially conform .to the inner surface of said base, a. coil of high resistance wire around said strip, means to attach the ends of said coil to said heater terminals so that said coil is connected across said heater circuit, and means to connect said cathode to the mid-point of said coil.

.6. In a vacuum tube of the heater type, a tubular cathode, a heater for said cathode, means within the base of saidtube to connect the cathode to a point electrically connected to ,the heater circuitbutspacedfrom the heater itself and having a potential equal to the average of the alternating potential of the filament.

In testimony whereof, Iaiiix my signature.

WALTER LOUIS KRAHL. 

